1. The Field of the Invention
The present invention relates to lockouts for load cell assemblies and fluid dispensing systems incorporating such load cell assemblies and lockouts.
2. The Relevant Technology
A load cell is a transducer that converts an applied force into a measurable electrical output. In turn, the electrical output can be used to calculate the applied force, such as the weight of an object. More specifically, a load cell includes one or more strain gauges through which an electrical current passes. When a force is applied to the load cell, the strain gauges deform which changes the electrical resistance produced by the strain gauges. The change in resistance is sensed by a central processing unit (CPU) which, by applying an algorithm, can calculate the force being applied.
Load cells are commonly used in a variety of different applications for measuring variable weight loads. For example, in the biopharmaceutical area, load cells are commonly used in association with containers used to produce cell culture media. The media is formed by mixing within a container predefined proportions of a powdered component and water. Because the media is often made as a large batch that is greater than 250 liters, load cells are associated with the container for measuring by weight the desired amount of water needed to produce the media. Once the proper amount of water has been delivered into the container, as determined by the load cells, the powder component can be added and then mixed with the water to form the media.
Depicted in FIG. 1 is one embodiment of a load cell assembly 10 commonly used in measuring the weight of a container 28 used to produce media. Load cell assembly 10 comprises a load cell 12, in the form of a load cell beam, having a first end 14 and an opposing second end 16. Load cell 12 is disposed between an upper support 19 and a lower support 18. Lower support 18 comprises a base plate 20 and a riser 22 disposed on base plate 20. First end 14 of load cell 12 is mounted on riser 22 so that second end 16 cantilevers over base plate 20. As depicted in FIG. 2, a transfer rod 24 extends between second end 16 of load cell 12 and upper support 19. Transfer rod 24 is used to transfer the entire load applied by upper support 19 onto second end 16 of load cell 12. FIG. 1 shows an annular seal 26 that encircles transfer rod 24 and is disposed between upper support 19 and load cell 12. Upper support 19 is secured to the floor of container 28.
During operation, the weight of container 28 is transferred to second end 16 of load cell 12 by passing through transfer rod 24. The resulting strain applied to load cell 12 is converted to an electrical signal which is transferred by an electrical cable 32 to a central processing unit (CPU) 33. In turn, by using the known weight of container 28, CPU 33 can calculate the weight and/or volume of fluid added to container 28.
Load cell assembly 10 also includes an anti-uplift bolt 34. Anti-uplift bolt 34 includes a bolt shaft 35 having a first end 36 with an enlarged head 38 formed thereat and an opposing second end 40. During assembly, second end 40 is freely passed down through a hole in upper support 19 and is then threaded into lower support 18. Anti-uplift bolt 34 secures upper support 19 to lower support 18 and thus prevents tilting or potential toppling of container 28. Anti-uplift bolt 34 can also be used for un-weighting load cell 12 when container 28 is empty. The un-weighting of load cell 12 enables container 28 to be serviced without risk of potential damage to load cell 12. Un-weighting load cell 12 is accomplished by tightening a first nut 42 against base plate 20 so that anti-uplift bolt 34 is rigidly fixed in place. A second nut 44 can then be threaded up bolt shaft 35 so as to push upper support 19 towards head 38. Second nut 44 is then repeatedly rotated about bolt 34 until the entire load applied by container 28 is transferred through bolt shaft 35 as opposed to through load cell 12. One example of load cell assembly 10 is the 0958 FLEXMOUNT® weight module provided by Mettler Toledo.
Although the prior art load cell assembly 10 functions for its intended purpose, it has a number of shortcomings. For example, second nut 44 on anti-uplift bolt 34 is located directly between supports 18 and 19 making it difficult to access. This inconvenience of location is compounded by the fact that the nut is small and often requires multiple turns to un-weight the load cell. Furthermore, anti-uplift bolt 34 is only designed to un-weight the load cell when the container is empty. The friction between second nut 44 on anti-uplift bolt 34 when the weight of the fluid is transferred onto the nut 22 makes it impractical to un-weight the load cell when the container is full of fluid. In addition, anti-uplift bolt 34 is so small that it would bend or otherwise fail if subject to a heavy load.
Accordingly, what is needed in the art are improvements to conventional load cell assemblies that solve all or some of the above shortcomings.